Plastic stopcock valves are used extensively in the medical arts, as well as various fluid handling industries. These inexpensive valves are normally discarded after use thus assuring a contamination-free valve while relieving personnel from the requirement of cleaning and reassembling the valves after each use.
Such valves typically consist of two pieces, i.e. a valve body and a core. The valve body is provided with a plurality of passage-containing extensions through which a fluid may be conducted. The core includes a conduit capable of putting two or more of the passage-containing extensions in fluid communication with each other when the core is rotated to a specific position in a bore provided in the valve body. By manipulating the core the direction and volume of flow through the valve is regulated. The core is interference fitted within the bore valve in the body by providing a core that is slightly larger in diameter than the bore. The interference fit produces radially directed forces that form a fluid tight seal between the core and the bore.
The radially directed forces are a function of the hoop stress (i.e., the force/unit area) generated by the slightly oversized core pressing against the bore. Of course, if the diameter of the core is much larger than that of the bore, even if the core can be assembled into the bore, the radial forces may be too large to allow rotation of the core within the bore of the valve body.
As mentioned above, the interference fit performs the function of sealing around the extension passages where they enter into the bore of the body such that fluid may pass from one passage, through the conduit means within the core and out another passage without any leakage between the core and the bore. Increased pressure created by fluid passing through the valve increases the hoop stress required to prevent leakage (i.e., the core must be of a larger diameter for a given bore diameter). However, as described above, this may lead to difficulty in rotating the core within the bore.
In addition, the above described valves may also experience crazing or micro-cracking when the valve is in use or has been stored for long periods of time. The presence of cracking in the valve renders the valve useless for most applications. The crazing and micro-cracking appears to be a result of the thinness of the valve body, the high interference fit required to properly seal the core in the bore when the valve is used with a high pressure fluid, and the pressure of fluid within the valve.
Another problem experienced with stopcock valves known as "flecking" occurs when portions of a soft core driven by the hoop stress creep into the passages in the extensions are sheared off by rotation of the core. Chattering or uneven movement is caused by hard or non-compliant core members.
It is therefore an object of the present invention to provide a stopcock valve wherein the stopcock core provides a high pressure seal within the body bore without inhibiting the rotation of the core within the valve body.
It is another object of the present invention to provide a stopcock valve which will be free of crazing and micro-cracking during reasonable storage or use.
It is yet another object to provide a low-cost easily assembled stopcock valve.
Yet another object of the present invention is to provide a stopcock valve provided with a core member that neither flecks nor chatters.
Other objects and advantages of this invention will become apparent from the following specification, claims and drawings.